Catalyst systems for the polymerization of olefins are well known in the art. Typically, these systems include a Ziegler-Natta type polymerization catalyst; a co-catalyst, usually an organoaluminum compound; an electron donor compound (optional), and an olefin monomer. Control of molecular weight is important as it influences the final physical properties of the polymer. The molecular weight is controlled by chain transfer reactions which terminate the growth of the polymer chains. A number of such chain transfer processes, including .beta.-H elimination, .beta.-alkyl elimination and chain transfer to MR.sub.n (M.dbd.Zn, Al, etc.), monomer, and hydrogen have been identified. Of these, hydrogen has been found to be the most practical chain transfer agent since it is generally easy to use and normally does not affect the activity of the catalyst. However, there are many cases where even hydrogen does not provide the optimum results due to some undesired side effects (e.g., unresponsive M--R bonds, overactivation of the catalyst, too rapid hydrogenation of other functional groups). Therefore, alternative chain transfer agents for use in the production of polyolefin homopolymers and copolymers, are highly desirable.
Terminally functionalized polymers are of great current interest. Such a polymer could be used as precursor for making block or graft polymers and would be expected to exhibit modified chemical and physical properties.
It has previously been disclosed in U.S. Pat. No. 5,578,690 that certain silanes can be used as chain transfer agents when ethylene, or a combination of ethylene and an .alpha.-olefin, is polymerized with certain metallocene catalysts. There the method resulted in an ethylene polymer, or co-polymer of ethylene and an .alpha.-olefin, having a silyl group at one terminus of its chain. Unfortunately, this organolanthanide polymerization system is limited to ethylene polymerization and copolymerization and cannot be expanded to homopolymers of higher .alpha.-olefins.